While McDermott -- who led the Panthers to top-10 finishes in yards allowed from 2012-15 -- should be able to help the Bills' sinking defense, he does not fix all of the problems for a team that has been as troubled as any during its 17-year playoff drought, especially in recent weeks.

Expectations for McDermott must be framed around the Bills' quarterback situation, which remains uncertain given the looming March 11 deadline to either guarantee a significant portion of Tyrod Taylor's contract ($27.5 million or $30.75 million, depending on whether the Bills exercise Taylor's option for 2018-21) or cut their two-year starter and begin yet another search for a starter.

What the Bills do with Taylor could depend on how much sway McDermott holds over personnel decisions. Indications in recent weeks were that general manager Doug Whaley appeared poised to move on from Taylor, but if McDermott was able to secure at least some control of the Bills' roster from owners Terry and Kim Pegula this week, the decision about Taylor will no longer rest solely with Whaley.

If the Bills ultimately decide to cut Taylor and start fresh at quarterback, expectations for McDermott should be low, especially in 2017. Without Taylor and with EJ Manuel set for unrestricted free agency in March, the Bills will be left with only 2016 fourth-round pick Cardale Jones and undrafted free agent Josh Woodrum on their roster at quarterback.

In that scenario, the Bills would need to select a quarterback in the early rounds of April's draft, or find a veteran to bridge the gap -- or do both. No matter what McDermott does to improve the Bills' defense or who he hires as offensive coordinator, the upcoming season could be arduous for a first-year head coach and a starting quarterback who could rank near the bottom of the NFL. Fans who gobbled up a franchise-record 60,000 season tickets when Rex Ryan was hired in 2015 would have to withstand short-term pain in hopes of long-term improvement.

The Bills' other option is to keep Taylor and attempt to build on a 7-9 performance this past season that Whaley believed was "close" to earning the Bills a playoff appearance. Despite his flaws and declining statistics in 2016, Taylor remains the Bills' best choice to start at quarterback in 2017. If his skill-position players stay healthier and McDermott can fix the broken defense, a 9-7 or 10-6 record seems reasonable.

Keeping Taylor would raise the expectations for McDermott and create more pressure to win in the short term. It is possible that such an approach succeeds, but over 29 starts, Taylor has not shown the consistency required to make him a top-tier quarterback in the NFL. Unless Taylor improves, the Bills' ceiling would seem to be a one-and-done wild-card playoff team, especially playing in the same division as the New England Patriots.

Outside of quarterback, the Bills' roster has other issues. The team has 28 players set to become free agents in March, and two starters -- safety Aaron Williams and defensive tackle Kyle Williams -- who have floated the idea of retirement. At positions such as wide receiver and safety, where free agency could hit the Bills the hardest, the team is devoid of young talent to fill the void.

Moreover, McDermott must find players who fit his 4-3 defensive scheme. The switch should benefit defensive ends Jerry Hughes and Shaq Lawson, who seemed out of place as outside linebackers in Ryan's system. The Bills, however, lack the speed and range required at linebacker in McDermott's scheme. Second-round pick Reggie Ragland, who missed all of his rookie season with a torn ACL, is a less-ideal fit in McDermott's scheme than in a 3-4 alignment, where he could play in a confined area as an inside linebacker. Preston Brown could also lack the range to play middle linebacker in McDermott's scheme.

After some cringe-worthy moments in recent weeks that made Buffalo one of the NFL's least-desirable landing spots for a head coach, credit the Bills for landing McDermott, who has eight years of coordinating experience.

But if recent history has taught Bills fans and observers anything, it is that disappointment often lurks around the corner.